Zirconia-containing silicate glass



1951 MOCKRIN ETAL 2,566,134

ZIRCONIA-CONTAINING SILICATE GLASS Original Filed Sept. 12, 1946 INVENTORS [5400/25 Mock/PIN BY Amvow c. Baa/5H A TTORNE Y.

Patented Aug. 28, 1951 .ZIRCONIA-CONTAINING SILICATE GLASS Isadore Mockrin, Philadelphia, Pa., and Arnold E. Pavlish, Columbus, Ohio, assignors, by mesne l assignments, to Holophane Company, Inc., New

York, N. Y., a corporation of Delaware Original. application September 12, 1946, Serial No. 696,606. Divided and this application April 11,1951, Serial No.222,003

1 Claim.

The present invention relates to. zirconiat-containing silicate glass, and is more particularly directed toward the manufacture of glass for use in pressed glass reflectors for controlling light for illumination, theglass having an index of refraction higher than that of the usual glass employed in such commercial articles.

'Owing to 'high clarity, the melting, pressing and working qualities, permanence and weathering and reasonable cost, glass of the silicasoda-lime type has heretofore been commonly used in the manufacture of pressed glassarticles such as reflectors, refractors and many other forms of pressed glass merchandise. Not only does this glass have these properties, but it is a comparatively light weight glass with an index of refraction of 1.5, a specific gravity of about 2.5 and a coefficient of expansion of approximately 85 times cm./cm./ C.

Not only does an increase in the refractive index of the, glass mean that there is a greater bending of the rays on entering the glass of a reflector, but there is a corresponding decrease in the critical angle of the medium. As the critical angle decreases, the width of the angular zone in which total internal reflection can occur is increased. Glass with higher index of refraction in illuminating reflectors has been desired because of its ability to control by reflection more of the light, but has not been used heretofore in commercial lighting reflectors. High index glasses, typically lead glasses, are used in optical work and in the manufacture of spectacular glassware, where costs permit and the undesirable qualities such as high Weight of such glass do not impair its usefulness in the particular instance. They, however, have one or more undesirable features rendering their use impractical for the purpose of the present invention. Glass for such purposes must be made at reasonable cost and it must be able to withstand operating conditions which the high index refraction glasses heretofore available, have been unable to satisfy.

The present inventionaims to produce glass Ill) for asuitableglass, investigationwas directed toward the substitution of. other oxides for silica so as to producea suitable glass of the desired index of refraction. .It is .well known that high index glasses. can be produced by the substitution of numerous oxides for silica, butthe-resulting glasses are objectionable for the purpose of the present invention owing to their weight, workability, expansion, and color. In this work glasses were developed which eliminated the objectionable features of the wellknown glasses.

Titania in amountsnp to;30% was found to produce progressively. increasing index of refraction with a tendency toward yellow or-amber color, and zirconia inamounts up .to nearly-30% produced a greenishjglass with moderate increase in indexof refraction.

The index of refraction increases in accord ance with the amount of titania orzirconia employed in the=glass,yetthe increase obtained in index where there was less than 10%of either or both of these oxides, is too small to be of economic advantage in increasing the output of reflected light from articlesmade from the glass composition.

While titania has more effect on the index than the zirconia, it affects the color of the glass tending to make it somewhat yellow and further investigations indicate that the substitu; tion of barium-oxide for some of the lime would make an improvement in the color.

In making up, glass for the purpose, the "raw materials used for the silica, sodium, calcium, magnesium and bariumcompounds will be of the usual. grade of purity 'commonly employed in manufacturing glass of this character, and the zirconium and titanium compounds can also be of commercial grade, preferably low in iron, aluminum or other metal of reducing nature.

As the glass batches employed in carrying out the present invention are related back to silicasoda-lime. glass, one can assume that theformulations employed are based on the substitution of either ZrOz or TiO2, 'or"both, for SiOz, the substitution of K20: for'part. of the NazO, and the substitution ofBaO or MgO in varying proportions for the CaOof the typical formula. This'typical orbasic formula for the silica-sodalime glassbased on weight of oxides canbe approximately 73% S102, approximately 1.7 NazO and approximately 8% CaO and approximately 2% minor ingredients. For the NazOone can substitute varying amounts or K20 up to not more than 12%. It was also found that substitution of K20 for some of the NazO would make an improvement in the color. The alkalis, NazO and K20, singly or combined, should range from about to about 27.5% and the alkaline earths singly or combined should range from 0% to about 12.5%.

In as much as the effect on the index of refraction of the addition of TiOz or ZIO2 is not of enough practical consequence in percentage less than (by weight) of either or of both combined, there would always beat least 10% of titania or zirconia substituted for silica and as the upper limit of zirconia and titania imposed by color and unworkability of metal is in the region of about 25% to 30% for these elements singly or combined.

While it is possible to substitute titania or zirconia, singly, for silica in amounts up to about 25 to about 30%, titania. and zirconia cannot be added in combination with one another in any such amounts. The two oxides may be used in combination in percentages totaling up to about 30%, and the most desirable glasses were produced when not more than of each oxide Was used. At least 10% of each oxide was found to be essential in order to provide a commercially advantageous increase in the index of refraction.

Excellent results have been obtained from glass compositions employing 15% TiO2, 9 /2% BaO, 57 SiO2 and 18% alkali, all of which may be NazO or up to 6% K20.

The various constituents required for the formulation are thoroughly mixed and the batch melted in substantially the same way as the ordinary silica-soda-lime batch, care being taken to maintain an oxidizing atmosphere. This material can be worked in very much the same manner as the silica-soda-lime lass and manufactured into pressed glass articles in the same way.

It has substantially the same characteristics in the melting, working and molding operation and has substantially the same weathering and permanence qualities, a specific gravity of 2.7 to 2.95. a coeificient of expansion of approximately 85 times 10* and indexesof refraction which range from 1.57 to 1.65.

The value of a higher index of refraction than that customarily used for prismatic reflectors is indicated in the accompanying drawings in which Figure 1 is a section illustrating reflector profile and Figure 2 is a section illustrating prism contour.

Figure 1 shows a typical prismatic reflector as used for lighting purposes in factories and many other working areas. The figure shows the reflector l, one-half in section, and the lamp 2 within the reflector with light center 3. Light rays emanating from 3 strike the inside surface of the reflector 4 and pass through to the prisms on the outer surface 5 where they are reflected twice and returned back through the inner surface 4 to pass out of the open mouth of the reflector. Typical light rays 6, 1, and 8 are indicated in this process of reflection.

The operation of these prisms is shown in Figure 2. This is a horizontal cross section through the wall of the reflector with the prisms on the outside. Light ray 2] comes from the center of the lamp filament, strikes the inner surface 4 of the reflector and passes through to the outer surface where it strikes one side of the prism. Typically, this prism is a 90 prism and the light ray 2| strikes the prism at an angle of incidence of 45, this being the angle between the ray and the normal to the surface. The normal is ndicated by dotted line 26. With an index of refraction of approximately 1.5, which is typical in glass used for prismatic reflectors, the critical angle is 42. Consequently any light'striking a glass surface from within the glass at an angle of incidence greater than 42 is totally reflected. Light ray 2| is, therefore, totally reflected from the prism surface 22 and crosses over to the other side of the prism 23. Here, exactly the same action occurs and the light ray is totally reflected and sent back through the inner surface of the glass in the desired direction. In the horizontal cross section of Figure 2, the light ray is returned in exactly the direction from which it came, but in elevation there will be an angular difference between the entering light ray and the reflected light ray as indicated in Fig ure 1.

The lamp filament 3 is not a point and due to its physical size, some light rays strike; thereflector at angles other than indicated for light ray 2|. Light rays 24 and 25 are indicated as coming from extreme edges of the lamp filament 3. These light rays pass into the glass at the inner surface 4 and are refracted slightly. Light ray 25 strikes the outer surface of" the prism at an angle of incidence somewhat less than that of light ray 2! as indicated in the figure. If this difference in angular direction of the two rays in glass is 3 or less, light ray 25 will still be reflected from the inner surface 22 of the prism because the angle of incidence will be 42 or greater. However, when the angle between light rays 2| and 25 in glass becomes substantially greater than 3, the angle of incidence is then materially less than 42 and a large part of the light of light ray 25 will be transmitted as indicated by the emerging light ray 25'.

Light ray 24 on the other hand will strike the surface 22 of the prism at angles of incidence greater than 45; consequently, light rays of which 24 is typical, will always be reflected from this surface 22. When this light ray i reflected over to the other side of the prism 23 it will be on the wrong side of light ray 2| for total reflection, and if 2! and 24 are more than 3 apart the light ray 24 will be transmitted as indicated by 24'. Some of this light 24' will enter the next prism and may be recovered but some of it will not enter this prism and, in any event, there will be losses through additional refraction and reflection and absorption. Therefore, for purposes of reflection, with an index of refraction of 1.5, such light rays as 2 3 and 25 are likely to be lost when the lamp filament 3 is large enough to produce a spread of more than approximately 3 each side of the central ray after the light has entered the first surface of the glass. Filaments of this size are commonly encountered and it is desirable to overcome this element of inefiiciency in prismatic reflectors.

The inefficiency may be overcom by increasing the index of refraction. For example, if the index of refraction is increased from 1.5 to 1.6 the critical angle is decreased from approxi mately 42 to approximately 39; consequently, the spread of light which will be reflected by the prisms is increased from 3 each side of the central ray in glass to 6. It is obvious that with lamp filaments of appreciable size, such an increase in the index of refraction of the glas will provide for the reflection of considerably more light than would occur with the original index of refraction.

This application i a division. of our applica- 5 tion, Serial No. 696,606, filed September 12, 1946, now Patent No. 2,554,952.

What is claimed is:

A clear, substantially colorless glass for illuminating glassware reflectors with an index of refraction of 1.57 to 1.65, a specific gravity of 2.70 to 2.95 characterized by the absence of color selective and light scattering components and consisting of 40% to 65% S102, alkali oxide component selected from the group consisting of NazO and K20 and mixtures thereof in amounts of from 5% to 27.5% with not more than 12% K20, alkalin earth oxide component selected from the group consisting of CaO, MgO and BaO 6 1 and mixtures thereof in amounts from 8% to 12.5%, an acid forming, high-index of refraction component amounting to from 10% to 30% of Zl'Oz and minor impurities not exceeding 2%.

ISADORE MOCKRIN. ARNOLD E. PAVLISH.

REFERENCES CITED The following references are of record in the file of this patent:

Eitel-Pirani-Scheel: Glastechnische Tabellen (1932) page 659. 

